Ms. Merkel, 58 and in power since 2005, will seek a third four-year term in national elections on Sept. 22. Until then, she wants to avoid rocking the boat with voters, who give her popularity ratings in the 60 percent to 70 percent range and seem quite content with the give-and-take, muddling-through approach she has adopted in the protracted euro crisis, often to the consternation of financial markets.